Apparatus and method for internally weld-cladding pipe elbows

ABSTRACT

The weld-cladding apparatus includes a turntable which is rotatably mounted in a yoke about a horizontal axis. An outrigger is mounted on the yoke and has a curvature coincident to the curvature of the torus-to-be-cladded and a center of curvature on the axis of the turntable. The weld-cladding means is rotatably mounted at the end of the outrigger in a vertical plane common to the plane in which the pivot axis of the turntable moves during rotation of the yoke. During use, the weld-cladding means remains vertical while the turntable pivots on the horizontal axis. In order to form a weld, the turntable is oscillated back and forth about the pivot axis over an arcuate length equal to the length of the torus. The turntable is tilted incrementally a distance equal to the width of a weld.

This is a division of application Ser. No. 865,155, filed Dec. 28, 1977,now U.S. Pat. No. 4,165,245.

This invention relates to an apparatus and method for the fabrication ofinternally weld-cladded toroidal bodies such as pipe elbows.

As is known, large pipe elbows generally consist of relatively thickferritic base structures for reasons of strength and economy and areprovided on the inside with austenitic weld-cladding for protectionagainst corrosion. In order to produce such elbows, flat sheets aregenerally hot-pressed in a die to form torus-sector half-shells. Thesehalf-shells are then heat treated and machined at the edges. Next, thehalf-shells are cladded internally and subsequently welded together intwo longitudinal seams. The welding operation is usually accomplishedfrom the outside in the following manner. First, the austenitic claddinglayers which protrude at the seam location in the outermost materiallayer, i.e., in the innermost layer of the half-shells, beyond the basematerial are welded tight by means of the TIG (tungsten inert gas)method. Next, the entire thickness of several millimeters of thecladding layer is filled by means of an austenitic welding material(Arosto 347).

In order to prevent carburization of the austenitic layer during asubsequent welding together of the ferritic base structures, it has beennecessary to lay down a so-called Kardo seam as an insulating layer.Such a seam consists of very low carbon material, the composition ofwhich, for example, reads in percent by weight: C-0.01; Mo-0.05;Si-0.05; Cu-0.045; P-0.01; S0.08 and the remainder iron (Fe). This Kardoseam protrudes outwardly beyond the cladding layer by a few millimeters,for example, three millimeters and thus extends substantially into thebase structure at the seam location of the half-shells to be welded.This Kardo seam has thereafter been followed by at least one manual seamof ferritic welding material. Thereafter, the seam location is filledup, preferably by a submerged arc welding technique.

However, the Kardo seam which protrudes into the ferritic base materialrepresents a discontinuity in the strength of the pipe elbow and must betaken into consideration in designing the wall thickness.

Further, in the known processes for joining the half-shells, thecross-section is generally distorted so heavily that the structure mustalso be straightened out afterwards. However, during this straighteningprocess, elongations and stresses are introduced. This can lead, in asubsequent annealing operation, to structure changes wherein detrimentalbrittle fracture properties can occur due to the formation of a coarsegrain.

Accordingly, it is an object of the invention to improve theconstruction of large toroidal bodies.

It is another object of the invention to improve the brittle fracturebehavior of a large pipe elbow formed of half-shells which are weldedtogether.

It is another object of the invention to avoid the need for a Kardo seamin welding two half-shells together to form a toroidal body.

Briefly, the invention provides an apparatus and method for internallyweld-cladding toroidal bodies such as pipe elbows.

The method comprises the steps of forming a pair of torus-sectorhalf-shells, machining the edges of each half-shell, subsequentlywelding the half-shells together into a toroidal body and straighteningand heat treating the toroidal body. Thereafter, the invention employsthe steps of applying a weld-clad along tangential generatrix lines onthe inside of the toroidal body and subsequently stress-annealing theweld-cladded toroidal body.

The method thus welds the half-shells prior to being weld-cladded. As aresult, the Kardo seam described above can be omitted so that thediscontinuities of strength mentioned above no longer occur. Inaddition, any coarse grain which may have formed when thewelded-together toroidal body is straightened out can be made a finegrain again in the subsequent stress-annealing step. This has not beenpossible with the previously known fabrication methods as describedabove since the already clad torus bodies must not be exposed to a highheat treatment temperature because this would lead to detrimentalcarburization of the austenitic cladding layer.

The heat treatment which is used includes an annealing of the toroidalbody at temperatures of 900° C. to 950° C. and a subsequent quenching inwater, oil or air. In addition, the step of stress-annealing includesheating of the toroidal body to a temperature of about 600° C. and asubsequent cooling in air.

The apparatus of the invention comprises a turntable for mounting of atoroidal body thereon, a means for tilting the turntable, a curvedoutrigger and a weld-cladding means mounted on the outrigger. Theturntable is rotatably mounted on a pivot axis while the tilting meansis constructed to rotate the turntable 360° about a horizontal axispassing perpendicularly through the pivot axis of the turntable. Thecurved outrigger is secured to this means and has a center of curvaturelocated on the pivot axis of the turntable. The weld-cladding means ismounted on the outrigger for rotation in a vertical plane relative tothe outrigger. In addition, the weld-cladding means is disposed in acommon vertical plane with the pivot axis of the turntable fordisposition within a toroidal body mounted on the turntable and a radiusof curvature corresponding to the curved outrigger.

The outrigger is detachably secured to the tilting means to permitreplacement by outriggers of different curvatures. This permits toroidalbodies with different curvatures to be weld-cladded on the apparatus. Inaddition, a means is provided for adjusting the outrigger relative tothe pivot axis of the turntable and to the plane of the turntable. Thispermits the outrigger to be adapted to toroidal bodies of differentcross-section diameters and/or wall thicknesses.

The weld-cladding means is also detachably mounted on the outrigger and,as such, facilitates the adjustment of the outrigger and the setting ofthe axis of rotation of the weld-cladding device relative to the core orlongitudinal axis of the toroidal body. In this regard, the pivot axisof the weld-cladding means on the outrigger is disposed in coincidencewith the longitudinal axis of the toroidal member, i.e., in the centerof the circle generating the toroidal body in each cross-section of thebody.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and accompanyingdrawings in which:

FIG. 1 illustrates an elevational view of an apparatus in accordancewith the invention; and

FIG. 2 illustrates a view taken on line II--II of FIG. 1.

Referring to FIG. 1, the apparatus for internally welding a toroidalbody such as a pipe elbow 11 has a pair of pillow blocks 2, 3 in which atilting means 4 is rotatably mounted via bearings 1. As shown, thistilting means 4 has a pair of side plates 5, 5' in which journals 6, 6'are mounted and journalled in the bearings 1. In addition, the tiltingmeans has a yoke 7 which extends between the side plates 5, 5'. Thecenter of the yoke 7 is provided with an eye 8 (FIG. 2) on an axisparallel to the principal direction of the side plates 5, 5'.

In addition, the apparatus has a turntable 10 which is rotatably mountedvia a pivot shaft 9 in the eye 8 of the yoke 7. Further, the pivot shaft9 is stepped at the free end and provided with a thread 12 (FIG. 2)which projects beyond the yoke 7. In order to rotate the turntable 10relative to the yoke 7, a worm gear 14 is mounted on the reduced end ofthe pivot shaft 9 in abutment with a shoulder (not shown) of the shaft 9and is secured against rotation by a key (not shown) and againstdisplacement by a nut 13 threaded onto the thread 12. The worm gear 14which is thus rotatable about the axis of the shaft 9 meshes with a worm26 of a reduction motor 28 mounted on the yoke 7 in suitable manner.This motor 28 is program-controlled in a manner (not shown), forexample, by a computer.

The height of the pillow blocks 2, 3 and the tilting means 4 are suchthat the turntable 10, including the super structures secured thereonand on the side plate 5', as described below, can be turned through anangle of 360° about the horizontal axis of the journals 6, 6'. Thishorizontal axis also passes perpendicularly through the pivot axis ofthe turntable 10 so that during the tilting of the turntable 10, theaxis of the pivot shaft 9 executes one revolution in a vertical plane22.

As shown in FIG. 1, the turntable 10, has a central cutout 20 and aplurality (e.g. 10) of radial mounting slots 21 for clamping of atoroidal body 11 to be weld-cladded thereon.

As shown, contrary to the journal 6, the journal 6' extends beyond thebearing of the pillow block 2. This extension carries a worm gear 25which is secured to the journal 6', for example by means of a key. Inorder to rotate the tilting means 4 about the horizontal axis, the wormgear 25 engages a worm 27 of a reduction motor 29. This reduction motor29 is program-controlled in a manner similar to the reduction motor 28.

A curved outrigger 35 is detachably secured to the tilting means 4 abouta center of curvature located on the pivot axis of the pivot shaft 9. Inaddition, a means is provided for adjusting the outrigger 35 relative tothe pivot axis and to the plane of the turntable 10. This means includesa plate 30 provided with a slot 31 through which a screw 24 passes intothe side plate 5' to hold the plate 30 on the side plate 5' and aslotted arm 34 of the outrigger 35. The slotted arm 34 is fastened onthe plate 30 by means of a screw 32 which threads into a region of theplate 30 outside of the slot 31. In addition, a spacer 33 is providedbetween the plate 30 and the arm 34. As shown, the outrigger 35 iscurved over most of its length and has a radius of curvaturecorresponding to the radius of curvature of the toroidal body 11. Forbodies 11 of different radii of curvature, differently curved outriggers35 are provided. Accordingly, the mounting of the outriggers 35 to thetilting means 4 is made detachable to permit ready replacement.

A weld-cladding means 37 is detachably mounted on the outrigger 35 forrotation in a vertical plane relative to the outrigger 35. As shown, theweld-cladding means 37 is disposed at the free end of the outrigger 35so as to be disposed in common with the pivot axis of the turntable 10in the vertical plane 22. The mounting is such that the weld-claddingmeans 37 is rotatable relative to the turntable 10 and the tilting means4. The weld-cladding means 37 receives welding material in ribbon formfrom a roll 40 which is rotatably mounted on the outrigger 35.Alternatively, in order to guide the ribbon in a simpler manner, theroll 40 may be disposed on an axis parallel to the pivot shaft 9 ratherthan in perpendicular relation as shown so that the surface of theribbon is perpendicular to the turntable 10.

The spacer 33 between the plate 30 and arm 34 may consist of anelectrically non-conductive material and the screw 32 can be surroundedby or underlayed with an insulator so as to provide a means forelectrically insulating the outrigger 35 from the tilting means 4 andthe turntable 10. In this case, welding current can be fed via theoutrigger 35 to the weld-cladding means 37. This can be accomplished inany suitable manner and is not further described.

The weld-cladding means 37 can be controlled in synchronism with thereduction motor 29 in such a manner that the principal axis of theweld-cladding means 37 always remains vertical in space. However, it isalso possible to reset the vertical position of the cladding means 37 inthe vertical plane 22 prior to each operation thereof. This is alwayspreceded by an incremental movement or step of the turntable 10 in thetilting direction.

As shown in FIG. 1, the toroidal body forms a 90° angle and is clampedto the turntable 10 by means of three clamps 42 in such a manner thatthe axis of curvature of the body 11 is coaxial with the pivot shaft 9.By shifting the plate 30 and the are 34 in the ranges permitted by theslots, the outrigger 35 can be set so that the pivot point of theweld-cladding means 37 coincides with the longitudinal axis, i.e., thecenter of the circle generating the toroidal surface of the shaped body11. Thus, when the table 10 rotates, the pivot point of theweld-cladding means 37 is always located on the core axis 23 of the body11 as the body 11 rotates about the axis of the pivot shaft 9.

In order to fabricate a toroidal body such as a pipe elbow 11, thefollowing steps are carried out. First, two torus-sector half-shells arefabricated from suitably cut sheets in a known manner by die forging.These half-shells are then machined at the longitudinal edges, i.e.,prepared for a subsequent welding operation, for instance, by deburringand cleaning the edges so as to provide the edges with a surfacesuitable for welding. The surfaces are then welded together to form atoroidal body of the two half-shells. In order to remove any deformationthat may have occurred during welding, the toroidal body 11 is thenstraightened out and subsequently heat treated for tempering or removalof stresses due to the straightening operation. This heat treatmentconsists of annealing of the toroidal body at temperatures of 900° C. to950° C. and a subsequent quenching in water, oil or air.

Thereafter, the toroidal body is aligned on the turntable 10 with theaxis of the curvature of the body 11 parallel to the axis of the pivot9. The body 11 is then fastened by means of the clamps 42. Unless theoutrigger 35 and the weld-cladding means 37 are already mounted and setup with the welding means 37 in the vertical plane 22, as would be thecase in the fabrication of a number of elbows with the same shapes anddimensions, the outrigger 35 is selected according to the curvature ofthe toroidal body 11 and is mounted and adjusted on the side plate 5' bymeans of the plates 30, 31. The adjustment is such that the weldingmeans 37 is located with its center of rotation in the vertical plane22, and more specifically, in the center of the circle generating thetoroidal body 11. During this adjustment, the welding means 37 canadvantageously be removed from the outrigger 35 if the center ofrotation of the welding means 37 is marked at the outrigger 35. The body11, outrigger 35, and welding means 37 are then mutually aligned so thatthe pivot point of the weld-cladding means 37 is located on the coreaxis 23 of the toroidal body 11 when the turntable 10 rotates about theaxis of the shaft 9. However, it is also possible to arrange theweld-cladding means 37 eccentrically of the axis of the shaft 9. Thisrequires the pivot point to the reset after each incremental tilting ofthe turntable 10 in the tilting direction.

The cladding layer is then applied in incremental steps. To this end,the turntable 10 is rotated about the axis of the shaft 9 by an anglewhich corresponds at least to the angle defined by the toroidal body 11.This constitutes a working forward stroke during which material isapplied. The turntable is then rotated in the opposite direction. Thisconstitutes an idle reverse stroke during which material is not applied.Between each two working strokes, the inclination of the turntable 10 ischanged in the tilting direction in accordance with the width of thecladding. This is carried out by an incremental tilting of the table 10about the axis of the journals 6, 6' via the reduction motor 29 andgears 27, 25. During this time, the position of the weld-cladding means37 is automatically changed relative to the outrigger 35 in the oppositedirection or must be readjusted by hand so that the cladding means 37retains a vertical position for each working stroke. If required, awelding powder funnel which is provided at the welding means 37 can berefilled between the two working strokes. Alternatively, an automaticfeed for the powder may be provided.

After applying the weld-clad along the tangential generatrix lines onthe inside of the toroidal body, the body 11 is stress-annealed. Thisstep can be accomplished by heating the finished pipe elbow or toroidalbody 11 to about 600° C. and subsequently cooling the elbow in air.

What is claimed is:
 1. An apparatus for internally weld-claddingtoroidal bodies, said apparatus comprisinga rotatably mounted turntablehaving a pivot axis for mounting of a toroidal body thereon; means fortilting said turntable 360° about a horizontal axis passingperpendicularly through said pivot axis; a curved outrigger secured tosaid means, said outrigger having a center of curvature located on saidpivot axis; and a weld-cladding means mounted on said outrigger forrotation in a vertical plane relative to said outrigger, saidweld-cladding means being disposed in a common vertical plane with saidpivot axis of said turntable for disposition within a toroidal bodymounted on said turntable and having a radius of curvature correspondingto said curved outrigger.
 2. An apparatus as set forth in claim 1wherein said outrigger is detachably secured to said tilting means. 3.An apparatus as set forth in claim 1 which further comprises means foradjusting said outrigger relative to said pivot axis and to the plane ofsaid turntable.
 4. An apparatus as set forth in claim 1 wherein saidweld-cladding device is detachably mounted on said outrigger.
 5. Anapparatus as set forth in claim 1 which further comprises means forelectrically insulating said outrigger from said tilting means and saidturntable.
 6. An apparatus as set forth in claim 1 in combination with atoroidal member having a longitudinal axis coincident with an axis ofrotation of said weld-cladding means on said outrigger.
 7. An apparatusas set forth in claim 1 wherein said turntable includes a plurality ofradial mounting slots for clamping of a toroidal member thereon.
 8. Anapparatus as set forth in claim 1 wherein said outrigger is detachablysecured to said tilting means and said weld-cladding device isdetachably mounted on said outrigger, and which further comprises meansfor adjusting said outrigger relative to said pivot axis and to theplane of said turntable and means for electrically insulating saidoutrigger from said tilting means and said turntable.
 9. A method ofinternally weld-cladding a toroidal pipe elbow which comprises the stepsofclamping the pipe elbow on a rotatable turntable having an axis ofrotation disposed in a vertical plane; placing a fixedly mounted curvedoutrigger with a center of curvature located on said axis and a radiusof curvature corresponding to the pipe elbow within the pipe elbow;mounting a weld-cladding means on the outrigger within the pipe elbowfor rotation in a vertical plane relative to the outrigger, saidvertical plane being disposed in a common vertical plane with said axisof the turntable; rotating the turntable about said axis by an anglecorresponding at least to the angle defined by the pipe elbow relativeto the outrigger while applying a cladding layer from the weld-claddingmeans along a tangential generatrix line on the inside of the pipeelbow; subsequently tilting the turntable about a horizontal axispassing through said axis of rotation in accordance with the width ofthe cladding layer; and thereafter sequentially repeating said steps ofrotating the turntable and tilting the turntable while retaining theweld-cladding means in a vertical position until the inside of the pipeelbow is weld-cladded.
 10. A method as set forth in claim 9 wherein therotation of the turntable constitutes a forward stroke and which furthercomprises the step of rotating the turntable in an opposite direction tosaid forward stroke during said step of tilting.
 11. A method offabricating a weld-cladded layer in a toroidal pipe elbow, said methodcomprising the steps ofclamping the pipe elbow on a rotatable turntabledisposed to pivot about a horizontal axis and to rotate about a givenaxis of rotation, said pipe elbow being positioned with a center thereofcoincident with said axis of rotation; placing a curved outrigger havinga radius of curvature corresponding to the radius of curvature of thepipe elbow at a level relative to the turntable and holding theoutrigger in fixed relation to said axis of rotation and to said levelduring rotation of the turntable for applying individual claddinglayers; pivotally mounting a weld-cladding means on the outrigger in thevicinity of the vertical pivot plane of said axis of rotation forpivoting in said pivot plane relative to the outrigger; and moving theturntable to and fro about said axis of rotation at least once over anangle corresponding to the arc of the pipe elbow while applyingindividual cladding layers from the weld-cladding means on the innersurface of the pipe elbow along coating lines of the elbow.